1. Field of the Invention
The present invention relates to display devices and methods for manufacturing and controlling the display devices, and in particular to a display devices using a current-driven light emitting elements and methods for manufacturing and controlling the display devices.
2. Description of the Related Art
Image display devices in which organic EL elements (also known as organic light emitting diodes, or OLEDs) are used, that is, organic EL displays are known as image display devices with which current-driven luminescence elements are used. Organic EL displays are attracting attention as candidates of the next-generation flat panel display (FPD) because they have advantages of good viewing angle properties and small power consumption.
In a usual organic EL display, organic EL elements which serve as pixels are arranged in a matrix. An organic EL display is called a passive-matrix organic EL display, in which organic electroluminescence elements are provided at intersections of row electrodes (scanning lines) and column electrodes (data lines) and voltages corresponding to data signals are applied to between selected row electrodes and the column electrodes to drive the organic EL elements.
On the other hand, an organic EL display is called an active-matrix organic EL display, in which thin film transistors (TFTs) are provided at intersections of row electrodes (scanning lines) and column electrodes (data lines) and connected with gates of driving transistors which receive data signals, when the TFTs are turned on through selected scanning lines, through the data lines and activate the organic EL elements.
Unlike the passive-matrix organic EL display, in which organic EL elements connected to selected row electrodes (scanning lines) emit light only until the selected row electrodes become unselected, organic EL elements in the active-matrix organic EL display keep emitting light until they are scanned (or selected) again; thus causing no reduction in luminance even when a duty ratio increases. Accordingly, the active-matrix organic EL display is operated at a low voltage, thereby consuming less power. However, a problem of unevenness in luminance occurs in the active-matrix organic EL display because luminance values are different among pixels due to a variation in characteristics of driving transistors or organic EL elements even when the same data signals are provided.
In conventional organic EL displays, such unevenness in luminance due to a variation or degradation in characteristics (hereinafter collectively referred to as unevenness in characteristics) of driving transistors or organic EL elements has typically been compensated by using complicated pixel circuitry or by feedback compensation using a representative pixel or the sum of currents flowing in all the pixels.
Using complicated pixel circuitry, however, reduces yields. Feedback compensation using a representative pixel or the sum of currents flowing in all the pixels cannot compensate unevenness in characteristics among pixels.
For these reasons, several methods have been proposed for detecting unevenness in characteristics among pixels using simple circuitry.
For example, in the electric optical device, the method for driving the electric optical device, the method for manufacturing the electric optical device, and the electric device which are disclosed in Patent Reference indicated below, the luminance of each pixel is measured using at least one kind of input current in an electric current program pixel circuit, the measured luminance ratio of each pixel is stored in a memory capacitor, image data is corrected based on the luminance ratio, and the electric current program pixel circuit is driven using the corrected image data. This suppresses unevenness in luminance, thereby achieving uniform display.
[Related Art Document]
[Patent Reference] Japanese Unexamined Patent Application Publication No. 2005-283816.